The invention relates to a controller for an internal combustion engine that can control a vehicle according to demand of a driver, even when a system for electronically controlling a throttle valve has trouble resulting in malfunctioning.
A control system for electronically controling opening and closing of a throttle valve is well known. Such a control system is generally called a DBW (drive by wire) control system. When the system has trouble, it is impossible to accurately control the throttle valve. Even when trouble has arisen, it is desirable that a minimum driving capability is ensured to move the vehicle to a safe turnout place or to a repair shop.
A mechanism has been proposed, which keeps the opening of the throttle valve constant to enable the vehicle to run when the control system has trouble. For example, the throttle valve controller disclosed in Japanese Patent Laid-Open No. 11-148406 has two kinds of turnout opening degrees for the throttle valve depending on whether the vehicle is in an idling state or not. After trouble has been caused in the throttle control system, if the accelerator opening detected is a first degree (for example, about 20%) or more that is sufficiently smaller than full opening degree, the throttle valve is set at the first degree. On the other hand, if the accelerator opening corresponds to that of the idling state or less, the throttle valve is set at a second degree (for example, a few percents) that is an opening with which air is introduced for keeping the engine in the idling state. The throttle valve controller has means that controls the ignition timing or the fuel supply volume to prevent the engine speed from becoming larger than a predetermined upper limit when trouble is encountered, the upper limit being sufficiently smaller than the permissible maximum rotational speed.
On the other hand, a gasoline internal combustion engine of a cylinder direct injection type has been proposed recently. The internal combustion engine of the direct injection type is switched between the uniform combustion and the stratified combustion. In the uniform combustion, the fuel is injected at the intake stroke and is diffused into the combustion chamber so that a homogeneous mixture is formed. In the stratified combustion, the fuel is injected at the compression stroke, forming a laminar mixture that is intensive around the ignition plug. In the case of the direct injection system, the range of the air fuel ratio allowing combustion is widened, and therefore, it is possible to minutely control the driving force generated by the engine by changing the air fuel ratio.
As a fail-safe measure to cope with situations where an internal combustion engine of a direct injection type has trouble, Japanese Patent Laid-Open No. 11-22531 describes a controller that judges permission to. switching to the stratified combustion mode. Specifically, the above-described controller has software means and a hardware judging circuit for judging permission to switching to the stratified combustion based on input signal relating to the engine operating conditions. Only when permission judgments of both of the above described software means and hardware judging circuit coincide, switching to the stratified combustion is allowed. According to this controller, when trouble has arisen, the throttle valve is fully closed, and switching from the stratified combustion to the uniform combustion is forcibly performed. At this moment, the air fuel ratio is set to the theoretical air fuel ratio or a lean air fuel ratio. Thus, deterioration of drivability due to undesired switching to the stratified combustion is avoided.
In the case of the throttle valve controller as shown in Japanese Patent Laid-Open No. 11-148406, when trouble has arisen in the control system for controlling the throttle opening, the area of the opening of the throttle is fixed, keeping the intake air volume to the engine constant. Thus, a driver cannot control the driving force generated by the engine. Furthermore, if an upper limit is provided to the engine rotational speed to regulate the rise of the engine rotational speed, the driver cannot control the driving force to be generated by the engine as well. Accordingly, for driving at the time of trouble, drivability becomes minimum.
Furthermore, as shown in Japanese Patent Laid-Open No. 11-22531, if the switching to the stratified combustion is prohibited and the target air fuel ratio is set at the theoretical air fuel ratio (14.7) or at a lean air fuel ratio ( greater than 14.7), the degree of flexibility to meet the demand of the driver is low if minimum drivability is ensured.
It is an object of the invention to enable a driver to control the driving force generated by the engine improving drivability, even when the system controlling the intake air volume to the internal combustion engine has trouble.
According to one aspect of the invention, the controller of an internal combustion engine detects demand variable indicating the demand of the driver, and controls the intake air volume to the internal combustion engine according to the detected demand variable. When trouble is detected in the system controlling the intake air volume, the controller switches the control of the vehicle to a turnout or emergency driving mode. In the emergency driving mode, the controller keeps the intake air volume to the internal combustion engine constant. Furthermore, the controller calculates the emergency driving control variable according to the above described detected demand variable, and controls the driving of the vehicle according to the above described calculated emergency driving control variable. Here, the emergency driving control variable is a control variable different from the above described intake air volume. Thus, in the emergency driving mode, it becomes possible to control the vehicle by a control variable different from the intake air volume ensuring a better drivability.
In one embodiment of the invention, the emergency driving control variable is the target air fuel ratio. The controller determines the target air fuel ratio from an air fuel ratio map provided for the emergency driving mode based on the detected demand variable and detected engine rotational speed.
In one embodiment of the invention, the above described demand variable is the opening or the degree of depression of the accelerator pedal. The controller calculates the intake air volume to the internal combustion engine according to the detected depression of the accelerator pedal. Based on the calculated intake air volume, the opening of the throttle valve is controlled by a throttle valve actuator. When the system controlling the intake air volume has a problem and when switching to the emergency driving mode takes place, the opening of the throttle valve is fixed at a full close or a nearly full close.
In another embodiment of the invention, the above described demand variable is the required torque according to the rotational speed of the internal combustion engine and to the opening of the accelerator pedal.
According to another aspect of the invention, the controller of an internal combustion engine has an accelerator pedal sensor that continuously detects the position of the accelerator pedal and an accelerator pedal switch that non-continuously detects the position of the accelerator pedal. When it is determined that the accelerator pedal sensor is not in trouble, the demand variable from the driver is calculated on the basis of the opening of the accelerator pedal detected by the accelerator pedal sensor. When it is determined that the accelerator pedal sensor is in trouble, the demand variable from the driver is estimated on the basis of the position of the accelerator pedal detected by the accelerator pedal switch. Thus, even when trouble has arisen in the accelerator pedal sensor, it is possible to realize a drivability that is nearly equal to that realized based on the demand from the driver.
In one embodiment of the invention, the accelerator pedal switch includes a full close switch that detects the full close state of the accelerator pedal. In another embodiment of the invention, the accelerator pedal switch includes not only the full close switch but also a full open switch that detects the full open state of the accelerator pedal.
According to another aspect of the invention, the internal combustion engine is a gasoline internal combustion engine of a cylinder injection system. The gasoline internal combustion engine of a direct injection system has an air fuel ratio of a wide range at which the engine can run. Accordingly, even when trouble has arisen, it is possible to minutely control the air fuel ratio, avoiding lowering of drivability.